Radiation from outer space containing charged particles can affect transistors in an integrated circuit (IC) resulting in a change in the state of transistors. This is called “Soft Error” or Single Event Upset (SEU). This type of error creates a temporary transient effect that corrupts logic within the IC. With the progress of microelectronics technology, the reduction in size of transistors allows for the integration of more transistors operating at lower threshold voltages within one IC. This makes the IC more vulnerable to soft errors.
SEU or soft error is a condition which may arise in the IC or system (chip) when it is exposed to high energy radiation (i.e., cosmic rays, alpha particles, neutrons etc.). This error manifests itself in the form of a change in state of a system from the normal expected state (e.g., change in the expected output of a combinational gate or a change of content of a state element from a 1 to 0 or vice versa). This may affect the outcome of the operation of the system. The effect of the error is temporary and if detected, the system can be restored to its normal operation by resetting the system or, if possible, by re-executing the system task. The error though temporary in nature, is of concern in mission critical operations (i.e., space, medical) where a downtime or delay for system recovery can be destructive.
When exposed to radiation, the devices on the chip are under constant bombardment by particles such as neutrons and alpha particles. When a high energy particle strikes a node in these devices, it generates electron hole pairs. Under the presence of a strong electric field, these charged carriers move toward their respective device contacts. If the collected charge is greater than the threshold value required for determining a logic level of a transistor, an erroneous value is registered. This minimum threshold value required to determine the logic level is also known as critical charge.